1. Field of the Invention
The invention relates generally to molded plastic containers of the kind currently used for a wide variety of products presently available in the consumer marketplace.
2. Description of the Related Art Including Information Disclosed Under 37 CFR .sctn..sctn.1.97-1.99
In general, plastic containers can be produced by a number of different procedures, including what are commonly known as extrusion blow molding, injection blow molding, and stretch blow molding. The disadvantages of some of these techniques reside in potential difficulty in manufacture, and excessive cost. In particular, extrusion blow molding is slow and expensive compared with injection blow molding and stretch blow molding. There are limitations to the type of plastic adaptable to each process, and often there are secondary or supplemental processing steps that must be performed in order to achieve the desired results, namely a finished, workable, cost-effective and reliable container.
Components produced by the above methods often suffer from limited uniformity in wall thickness and relatively wide dimensional tolerance, owing to dependence upon blowing the form into a mold from an extrusion tube and not being able to confine the plastic as it is taking shape between a mold and a force.
Injection blow molding enjoys the advantage of greater precision compared to extrusion blow molding, but also suffers limitations with respect to the type of plastics available for use in such a process. In particular, injection blow molding employs horizontal core rods to hold and transfer plastic components through multiple stages of manufacture. The viscosity of the resins while the components are still in a plastic state has been found to be critical in obtaining acceptable results. Thus, the choice of plastic is limited, and processing can become complex. Additionally, control of the processing temperature is difficult, since internal cooling of core rods is awkward to predict and regulate. Essentially the process depends upon forming a parison or preform, by injection molding around a core rod which thereafter carries the still-plastic parison to a blow molding station, where it is formed into its final shape or configuration. Finally the article is transferred to an ejection station, where it is removed from the core rod. Although wall thickness in this case is more precise than with articles produced by extrusion blow molding, a deflected core rod can result in undesirable wall thickness variations. A significant problem with injection blow molding is that of cost, since the initial installation is far more expensive than for extrusion blow molding. Molds for injection blow molding typically cost between 4 and 5 times that involved with equipment for extrusion blow molding.
Stretch blow molding requires an even greater investment in tools and machinery, and also is limited in its application to fewer polymers than is the case with extrusion blow molding, since the transfer of a parison to a blow mold station requires some viscosity considerations, even though the cores are in a vertical rather than in a horizontal position.
The following patents are cited as being of interest:
______________________________________ U.S. Pat. Nos.: ______________________________________ 3,244,312 3,885,701 3,887,316 3,938,687 4,251,001 4,356,926 4,372,459 4,572,851 4,610,394 4,931,329 ______________________________________
U.S. Pat. No. 4,572,851 discloses a two-part bottle where the individual parts are formed by stretch-type molding and thereafter joined together along a circumferential line. One of the parts or sections is telescopically received in the other, by a friction-fit, and the resultant joint formed as a "leak-proof friction weld", col. 6, line 47. An example of a suitable plastic is given in col. 7, line 7, as polyethyleneterephalate [sic]. The outer surface of the seam presents an external bead, FIG. 10, at the location of the seam.
U.S. Pat. No. 4,372,459 discloses a container constituted of joined cup-like sections, (with optional thin plastic coatings), and where adhesive is applied at the joint. The adhesive functions both to hold the sections together, and to "cover" the free edges of the members (col. 1, line 51) in the sealed condition of the container.
U.S. Pat. No. 4,356,926 discloses a two-piece container with a plastic upper section and a metal lower section. Heat fusion is employed to join and seal the sections together.
U.S. Pat. No. 4,931,329 illustrates a proposed construction which allegedly facilitates the re-cycling of a bottle by cutting sections out of it and adapting the resulting pieces to other uses. The disclosed device has the appearance of the 2 liter soft drink bottles currently in use, at least some of which are made by joining molded bottle halves along an axial plane.
Of the remaining patents noted above, U.S. Pat. Nos. '394 and '001 disclose containers having axial seams. U.S. Pat. Nos. '312, '687, and '701 relate to containers having separable upper and lower sections, at a transaxial or cross plane. U.S. Pat. No. '701 shows a tongue and groove configuration between a container's lid and body.
U.S. Pat. No. '316 illustrates an injection-blow molding apparatus for producing containers.